Research On Fly Ash Concrete Under Coupling Action Of Carbonization And Freeze Thaw Cycle

Concrete structure is the most widely used structure form currently,its durability has been paid highly attention in this region.All kinds of concrete durability damage are happened due to different working condition and environment.The single factor durability damage has been widely discussed by international scholars,while in practical engineering, concrete damage is caused not only for a certain factor,but by a combination of two or more factors.And the coupling action of these factors,is not a simple superposition,but the more complicated relationship that promote each other or restrict each other.In northern China,especially the servere cold region like Qinghai-Tibet and Northeast Region,almost all the buildings are eroded by carbon dioxide and suffered from freeze-thaw cycle,which seriously decrease the service life of buildings.On this foundation,concrete mixed with air-entraining agent is designed with the characteristic of high antifreeze in the paper,and the coupling action experiment is done in order to discuss the mechanism of concrete under carbonation and freeze-thaw.For further durability research,the servere cold region in China is divided into two types namely Qinghai-Tibet and Northeast Region.The concrete experiments were divided into five groups according to the the dosage of fly ash 0,10%,20%,30%,40% at the same water cement ratio of 0.4,and each group is divided into four experiments to study,including two coupling action tests namely carbonation before freeze-thaw mode(CF) and freeze-thaw before carbonation mode(FC),and two single tests namely single freeze-thaw test and single carbonation test.The test measurements include carbonization index(carbonation depth and carbonation area) and freeze-thaw index(mass loss rate and relative dynamic elastic modulus).The main research contents as follows:First of all, through rapid carbonization test,to explore the relationship between carbonization index and carbonization age,and different dosage of fly ash.Secondly,through rapid freeze-thaw test,to explore the relationship between freeze-thaw index and different freeze-thaw cycles,and different dosage of fly ash concrete.Finally,the coupling test of carbonation and freeze-thaw cycle,compare the CF and FC test results of carbonization index with single carbonization test,in order to discuss the influences of freeze thaw on the carbonization;compare the CF and FC test results of freeze-thaw index with single freeze-thaw test,in order to discuss the influences of carbonization on freeze-thaw.The results are show as follows:(1),Fly ash concrete mixed with air-entraining agent,carbonation damage and freeze-thaw damage are not a single case of both stack, but much more serious to each other;(2),The CF model,FC mode compared with the single carbonization experiment,carbonation depth is deeper and carbonation area is larger,that is,,freeze thaw cycle aggravate carbonation;(3),The CF model,FC mode compared with the single, freeze thaw experiment,mass loss rate is bigger and relative dynamic elastic modulus decreased faster,that is, carbonation aggravate freeze thaw cycle;(4),Fly ash concrete mixed with air-entraining agent has a high antifreeze ability,while its carbonation resistance ability is weak;(5),The method of using IPP software to measure carbonization area can be more accurate to analysis concrete carbonation rule after freeze and thaw, which is worth being promoted.